A simple, reliable, broadband method for extracting constitutive property measurements from an electromagnetic material sample occurs under plane wave conditions. Therefore, the ability to mimic a plane wave condition at the material sample is of paramount importance. Performing such measurements in a small spot-size and a broad band of frequencies allows designers and users of electromagnetic materials to reliably determine the constitutive properties of material samples as a function of position, particularly graded impedance and resistance sheets (such as those used to reduce diffraction from edges of parabolic dish antennas).